For example, Japanese Patent Laying-Open No. 4-222794 discloses a conventional crushing method for breaking rock or the like. FIG. 19 is a model diagram showing a conventional crusher. FIG. 20 is a model diagram showing the basic structure of the crusher shown in FIG. 19, and FIG. 21 is a partially enlarged model diagram showing the forward end of an electrode shown in FIG. 20. The structure and the operation of the crusher for carrying out the crushing method disclosed in the aforementioned Japanese Patent Laying-Open No. 4-222794 are described with reference to FIGS. 19 to 21.
First, the structure of the conventional crusher is briefly described with reference to FIGS. 19 to 21. A pulse power source 106 consists of a circuit including a capacitor 108, a switch 107 and the like. A power source 109 is connected to the pulse power source 106. The circuit of the pulse power source 106, a casing including this circuit and a car body carrying the crusher are grounded.
A coaxial electrode 101 serving as a breakdown electrode for breaking rock or the like is connected to the pulse power source 106 through a coaxial cable 105. A center electrode 112 and a peripheral electrode 115 located on the outer periphery of the center electrode 112 through an insulator 113 are arranged on the forward end of the coaxial electrode 101. One of the center electrode 112 and the peripheral electrode 115 is grounded, while charges stored in the capacitor 108 are guided to the other one when the switch 107 of the pulse power source 106 is closed.
The conventional crushing method is now described. A preliminary hole 110 is previously formed in the rock or the like to be broken with a drill or the like. An electrolyte such as water 111 is injected into the preliminary hole 110. The coaxial electrode 101 is inserted into the preliminary hole 110.
The power source 109 generates charges, which in turn are stored in the capacitor 108. A unilateral pole of the capacitor 108 is grounded.
The switch 107 is closed after the capacitor 108 sufficiently stores charges, thereby supplying the charges to the coaxial electrode 101 through the coaxial cable 105. Potential difference takes place between the center electrode 112 and the peripheral electrode 115 on the forward end of the coaxial electrode 101, thereby causing a discharge. At this time, the electrolyte is converted to plasma by discharge energy around the forward end of the coaxial electrode 101, thereby generating a pressure wave. This pressure wave breaks the rock or the like around the coaxial electrode 101.
The aforementioned Japanese Patent Laying-Open No. 4-222794 states that electric energy is supplied to the coaxial electrode 101 in a ratio of at least 100 MW per microsecond when crushing rock or the like until power having a peak value of at least 3 GW is obtained across two electrodes (the center electrode 112 and the peripheral electrode 115) of the coaxial electrode 101 dipped in the electrolyte in a confined region of the substance to be crushed.
The aforementioned conventional crusher has the following problem: The electrolyte is in a plasma state in a region where an arc is formed by the discharge between the center electrode 112 and the peripheral electrode 115, and the temperature of this region remarkably varies with the value of the current supplied to the coaxial electrode 101. In other words, the temperature of the region where the arc is formed is increased as the current value is increased. On the other hand, it is known that discharge resistance is reduced as the temperature of the region where the arc is formed is increased. The energy consumed by the discharge of the coaxial electrode 101 is proportionate to a value obtained by multiplying the square of the value of the current supplied to the coaxial electrode 101 by the discharge resistance.
Also when the value of the current supplied to the coaxial electrode 101 is increased for increasing the energy (energy utilized for crushing) consumed by the discharge of the coaxial electrode 101, therefore, the discharge resistance is reduced as the current value is increased. Thus, it is difficult to sufficiently increase the energy consumed by the discharge of the coaxial electrode 101 by simply increasing the aforementioned current value. In the conventional crusher, therefore, it is difficult to efficiently perform crushing by increasing the energy utilized for crushing.
The present invention has been proposed in order to solve the aforementioned problem, and an object of the present invention is to provide an electrode for a crusher and a crusher capable of increasing energy utilized for crushing.